It’s as simple as “make sure they are out of blockstun”. Doing a jumping S or pipe with haggar causes lots of blockstun, so you have to wait longer to command grab. If you force them to block a jumping light, you can almost immediately command grab them since the blockstun is so little.

The is why weskers will do crouching light a couple times before command grab. They get that frame trap making the opponent weary of trying to use pushblock (pushblock extends blockstun, and is harder to perform against light blockstun attacks) and by pressing buttons they know they could get combo’d. Up-back is defeated by these crouch lights as well, which is essentially the only way to avoid weskers 1 frame command grabs. If they become afraid of those lights and avoid up-backing, the command grab comes basically free. To avoid this, the opponent has to make a read or use a move that counteracts this (like ryu shoryuken would beat out the situation if you can time it right).

If your characters command grab doesn’t come out for 3 frames, you can activate it 2 frames before they leave blockstun and it will work if they don’t jump.

Any kind of stun (blockstun, hitstun, counter-hitstun, crumple) cannot be command grabbed out of. The only exception is haggars headbutt on a standing character (causes birds to fly over their head), which if you land this the only reason to abuse this exception is to use a command grab hyper (haggar lvl3)

And it’s specific to haggar. she-hulk command grab visually causes the same thing (birds flying over their head), but you cannot use command grabs after that.